The present invention relates to the field of plant molecular biology, more particularly cotton WRINKLED1-like (WRIL) genes whose encoded proteins act as transcription factors of genes involved in fatty acid biosynthesis. The present invention also relates to methods of increasing cotton fiber length in cotton. In one embodiment, the methods involve modulating the level of activity of an enzyme involved in a fatty acid biosynthesis in the host cotton cell and/or culturing the host cotton cell. In another embodiment, the methods involve the manipulation of transcription factors which can regulate a gene encoding an enzyme involved in fatty acid biosynthesis.
The publications and other materials used herein to illuminate the background of the invention or provide additional details respecting the practice, are incorporated by reference, and for convenience are respectively grouped in the Bibliography.
Cotton (Gossypium spp.) is the world's most important fiber plant and a significant oilseed crop, being grown in more than 80 countries with a record of 122 million 480-pound bales in world production during the 2006/2007 growing season (United States Department of Agriculture—FOREIGN Agricultural Service). The deficit between consumption and production has happened in 1994/1995 and is forecasted to continue to widen to 2.5 million 480-pound bales in the 2009/2010 growing season (United. States Department of Agriculture—Foreign Agricultural Service [USDA—FAS] 2009). Cotton production provides income for approximately 100 million families, and approximately 150 countries are involved in cotton import and export. Its economic impact is estimated to be approximately $500 billion/year worldwide. Moreover, modifying cotton-seed for food and feed could profoundly enhance the nutrition and livelihoods of millions of people in food-challenged economies. Cotton is also a potential candidate plant of renewable biofuel. Cotton fiber is composed of nearly pure cellulose. Compared to lignin, cellulose is easily convertible to biofuels. Optimized cotton fiber production and processing will ensure that this natural renewable product will be competitive with petroleum-derived synthetic non-renewable fiber to ensure more sustainable development.
At present, seeds are always the most important part used for human and animal nutrition for crops. Major seed storage compounds include such as triacylglycerol (TAG), proteins, and carbohydrates, which are typically making up most of the mass of mature seeds, and the proportions of these components have large species-specific variations. Since seed composition and yield are important traits for breeding and agricultural research, partitioning of carbon and nitrogen into the major storage products within the developing seed is an important process. In model plant Arabidopsis, one AP2-domain containing transcription factor WRINKLED1 (WRI1; At3g54320) controls the conversion of sucrose into triacylglycerol and showed a strong role in controlling carbon and nitrogen flux into TAG biosynthesis and accumulation (Cernac and Benning, 2004).
As the most important agronomic traits of cotton are fiber quality and yield it is important to improve our understanding of genes underlying cotton fiber development. Cotton fibers are single-celled seed trichomes and the developing cotton fiber is considered as an excellent model system for studying the dynamics and functions of the cytoskeleton (Seagull, 1990). It is important to investigate how dynamic changes of the cytoskeleton and the expression of cytoskeleton-related genes contribute to fiber development. Some progress has been made in this direction. GhActin, a cytoskeleton protein, has been proven to be important for fiber elongation but not fiber initiation (Li et al., 2005). Overexpression of a fiber-preferential actin-binding protein (GhPFN2) blocked cell elongation prematurely (Wang et al., 2010). On the other hand, down-regulation of the actin depolymerizing factor gene (ADF) has been reported to increase fiber length and fiber strength (Wang et al., 2009).
The ultimate objective of gene function analysis in cotton is to utilize them to increase cotton fiber yield and quality. At present, there are relative few genes which have been successfully used to transform cotton and increase cotton fiber yield and quality. Many of them come from carbohydrate biosynthesis genes. For example, the transgenic over-expression of sucrose synthase gene (sus and sps) and cellulose synthesis gene (acsA and acsB) improved cotton fiber length and strength (Ruan et al., 2003; Jiang et al., 2011;). Similarly, higher xyloglucan endotransglycosylase/hydrolase (XTH) activity can promote fiber cell elongation and transgenic cotton with over-expressed xth gene had increased mature fiber length (Lee et al., 2010). The overexpression of carbohydrate biosynthesis genes may partition fixed carbon toward carbohydrates thus increase cotton fiber yield and quality. It is interesting to find some transcriptional factors which can regulate the carbon flow between lipids and carbohydrates in reproductive organs of cotton. Work with Arabidopsis has shown that over-expression of an Arabidopsis WRI1 cDNA under the control of the cauliflower mosaic virus 35S promoter led to increased seed oil content (Cernac and Benning, 2004). On the other hand, seed oil accumulation in an Arabidopsis splicing mutant allele, wri1-1, was reduced. Glycolysis was compromised in this mutant, rendering developing embryos unable to efficiently convert sucrose into precursors of triacylglycerol biosynthesis (Cernac and Benning, 2004).
The availability of genetic resources and cotton gene sequences will facilitate the improvement of key agronomic traits of cotton. To this end, a public effort was initiated in 2007 to determine the complete cotton genomic sequence. While this effort is underway there is an ever-expanding set of Gossypium EST sequences (about 400,000 now) being deposited in the public database. Notwithstanding the availability of such a huge amount of cotton gene sequences the functions of only a small number of genes have been identified. This is mainly because large scale analysis of cotton gene function has been constrained by the laborious and time-consuming process of generating transgenic cotton. Moreover, many cotton cultivars are recalcitrant to genetic transformation. Therefore, there is an urgent need to develop a rapid method for species independent functional analysis of Gossypium genes on a genomic scale.
Virus-induced gene silencing (VIGS) offers an attractive alternative to transgenic technology as it allows the investigation of gene functions without plant transformation (Ruiz et al., 1998; Burch-Smith et al., 2004). A partial fragment of a candidate gene is inserted into the virus vector to generate a recombinant virus. Infection of plants with this recombinant virus leads to the production of virus-related small interfering RNAs (siRNAs) (Baulcombe, 2004), which can mediate degradation of related endogenous gene transcripts, resulting in silencing of the candidate gene expression in inoculated plants (Brigneti et al., 2004; Burch-Smith et al., 2004). The silencing effect on endogenous gene expression can usually be assayed 1-2 weeks after virus inoculation. VIGS has become one of the most widely used and indeed important reverse genetics tools, especially for non-model plants.
It is desired to identify genes that are involved in biosynthetic pathways that the modulation of which may lead to increased cotton fiber length. It is also desired to develop methods for increasing cotton fiber length.